Flat commutator structure

ABSTRACT

A flat commutator structure having commutator segments which are made by stamping from sheet material and at their ends facing the shaft are anchored in a hub made of a synthetic material by injection moulding. To increase the flatness of the commutator face the commutator segments are also interconnected by anchoring elements near the outer periphery of the commutator. Both the hub and the latter anchoring elements may form parts of a single commutator support made from a synthetic material by injection moulding and preferably have open chambers into which the grooves separating the commutator segments terminate.

United States Patent Van De Griend [4 1 May 22, 1973 [54] F LAT COMMUTATOR STRUCTURE [75] Inventor: Jan Maarten Van De Griend, Dordrecht, Netherlands [73] Assignee: U.S. Philips Corporation, New

York, NY.

- [22] Filed: Sept. 13, 1971 [21] Appl. No.: 180,027

[30] Foreign Application Priority Data Sept. 23, 1970 Netherlands 7014025 [52] US. Cl ..310/235, 310/237 [51] Int. Cl. ..H0lr 39/16 [58] Field of Search ..310/235, 233, 236, 310/237, 219, 220, 222

[56] References Cited UNITED STATES PATENTS I 1,901,955 3/1933 Giaimo ..310/237 3,005,920 10/1961 Dolza 3,488,538 l/1970 l-layashi ..3l0/220 3,487,248 12/1969 Kaneko ..310/220 3,617,785 11/1971 Kristiansen ..3l0/236 Primary ExaminerR. Skudy AttorneyFrank R. Trifari [5 7 ABSTRACT A flat commutator structure having commutator segments which are made by stamping from sheet material and at their ends facing the shaft are anchored in a hub made of a synthetic material by injection moulding. To increase the flatness of the commutator face the commutator segments are also interconnected by anchoring elements near the outer periphery of the commutator. Both the hub and the latter anchoring elements may form parts of a single commutator support made from a synthetic material by injection moulding and preferably have open chambers into which the grooves separating the commutator segments terminate.

8 Claims, 3 Drawing Figures Patented May 22, 1973 2 Sheets-Sheet 1 Fig.1

INVENTOR. JAN M. VAN DE GRIEND i-wx P.

Patented May 22, 1973 2 Sheets-Sheet 2 INVENTOR.

JAN M. VAN DE GRIEND Agent FLAT COMMUTATOR STRUCTURE The invention relates to a flat commutator structure for use in a small electro-dynamic machine comprising a plurality of collector segments made of sheet metal which are insulated from each other and at the shaft ends are anchored in an injected hub made from a synthetic material.

The term a hub injected from a synthetic material" is used by those skilled in the art to mean a hub which is made by injection moulding in a mould in which previously the collector segments have been placed, so that on termination of the injection moulding process given portions of the segments are embedded in the hub material.

This construction is known. It has several characteristic advantages over collector structures which comprise a disc of insulating material which is provided with segments by electrodeposition and which are frequently referred to as printed commutators. A first advantage consists in the freedom in respect of the choice of the material of the contact layer. When electrodeposition is used, this choice is greatly restricted. The same applies to the nature of the surface, the mechanical properties and the structure of the contact layer.

So far as we know, in high-quality small direct current motors suitable for use in sophisticated apparatus, such as portable cassette tape recorders, hi-fi gramophone record players, etc., at present printed commutators are invariably used in conjunction with resilient metal brushes, which exert very low contact pressures. The speed of these motors is electronically regulated and for the speed regulation it is of the greatest importance that the effective contact resistance between the brushes and the collector should be as constant as possible in operation, since all changes in this resistance involve speed variations.

The effective contact resistance is influenced by the choice of the materials of the contact surfaces of the commutator and the brushes, by the contaminations which lodge between the said contact surfaces, inter alia owing to wear, and by the degree in which the resilient metal brushes dance on the collector surface. This dancing is a dynamic phenomenon which consists in that in operation the brushes may vibrate so that the contact faces of the commutator segments and of the resilient brushes are not in continuous contact. If the contact faces are in contact with one another for the major part of the time, the effective contact resistance is smaller than when they are in contact with one another for a minor part of the time.

Consequently, a high rate of dancing means an increased effective contact resistance. This adversely affects the desired constancy of the contact resistance in an indirect manner, for an increased effective contact resistance means that higher current densities are required at the contact faces of the commutator and the brushes. This results in faster wear and hence reduces the life of the motor, but it also means increased contamination of the contact surfaces by wear particles, and these again may give rise to increased dancing" and may cause short circuits between the commutator segments, which renders electronic control impossible.

Thus, an important factor in assessing the quality of a commutator construction suitable for use in technologically advanced products consists in the difference in height between the commutator segments on either side of the commutator grooves separating them. Practice has shown that this difference should not exceed 8 microns, since otherwise excessive dancing occurs.

Another factor is that the distance of the commutator contact faces and the brushes from the motor shaft should be a minimum, for with a small distance the relative speed of the contactsurfaces and hence the wear is low.

These quality requirements are satisfied by the known commutator constructions of the type described at the beginning of this specification in a far smaller degree than by the aforementioned printed commutators. It is difficult to reduce the diameter of the injected hub and to achieve at the same time such anchoring of the commutator segments in the hub that the height differences between the segments do not exceed 8 microns.

However, the invention provides a commutator construction of the type mentioned at the beginning of this specification, in which these disadvantages are obviated and which is characterized in that the collector segments are interconnected by anchoring elements near the outer periphery of the commutator also.

The anchoring elements at the outer periphery enable the commutator to be of a flatter structure than has been possible hitherto. Moreover, their provision enables the hub diameter and hence the distance of the contact faces of the commutator and the brushes from the motor shaft to be reduced.

For obtaining minimum height differences between the commutator segments an embodiment is of importance which is characterized in that anchoring elements of the said kind anchor the commutator segments immediately on either side of the slots between them.

Preferably a commutator construction in accordance with a further embodiment of the invention is used, which is characterized in that the hub and the said anchoring elements form part of a single integral commu tator support made of a synthetic material by injection moulding.

In order to counteract the accumulation of wear particles and other contaminations in the commutator grooves, another embodiment of the invention is of importance which is characterized in that the grooves between the commutator segments open into open chambers of the commutator support. Another important advantage of this embodiment will become apparent upon consideration of the detailed description with reference to the figures.

To prevent sparking between the brushes and the commutator segments still another embodiment of the invention will frequently be attractive, which is characterized in that there is mounted on the hub a discshaped anti-interference member and in that each commutator segment has a lug which is situated at the outer periphery of the commutator about midway between the two adjoining commutator grooves and is bent axially and is anchored to, and passes through, the commutator support so as to make contact with the antiinterference member.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is an elevation of a commutator structure according to the invention enlarged to ten times the actual size and viewed from the commutator side,

FIG. 2 is an equally enlarged sectional view of the commutator structure of FIG. 1, and

FIG. 3 is an elevation, enlarged to twice the actual size, of part of a metal strip in the form it has after several stamping operations, which strip is an intermediate product in the manufacture of the commutator structure shown in FIGS. 1 and 2.

In the Figures corresponding parts are designated by the same reference numerals.

The commutator structure shown in FIG. 1 comprises three commutator segments 1, 2 and 3 made of sheet material and anchored at the ends nearer the shaft in a hub 4 which is made of a synthetic material by injection moulding. Near the outer periphery of the commutator the commutator segments are interconnected by anchoring elements 5, 6 and 7. These anchor the segments immediately on either side of commutator grooves 8, 9 and 10.

FIG. 2 shows, more clearly than does FIG. 1, that the hub 4 and the anchoring elements 5, 6 and 7 form parts of an integral commutator support 11 which is made of a synthetic material by injection moulding. This Figure also shows clearly that the commutator groove opens into an open chamber 12 in the commutator support 11. The other collector grooves also terminate in such open chambers.

On the hub, there is arranged a disc-shaped antiinterference member 13 of a known type which comprises a disc made of material having a voltagedependent resistance value on either major surface of which a conductive pattern is provided.

The commutator segments 1, 2 and 3 each have near the outer periphery of the commutator and about midway between the two adjoining commutator grooves a lug 14, 15 and 16, respectively, which are bent over axially. These lugs are anchored in the commutator support 11 and protrude through it so as to make contact with the anti-interference member 13. The latter is urged against the ends of the lugs l4, l5 and 16 by a slotted cup-spring 17 mounted on the hub 4.

In the part of the metal strip 18 which is shown in FIG. 3, the commutator segments 1, 2 and 3 and the lugs 14, 15 and 16, which have not yet been bent over, can already be distinguished. The strip 18 is an intermediate product in the manufacture of the collector structure shown in FIGS. 1 and 2, and the Figure shows the shape of the strip after it has been subjected to all the stamping operations which precede the injection moulding of the commutator support. The strip 18, which is made of phosphor bronze, is covered with a layer 19 of a noble-metal alloy by rolling.

After the lugs l4, l5 and 16 have been bent over, three commutator supports 11 are simultaneously made in a single operation in the injection moulding machine. After the injection moulding process, the commutators are stamped from the strip and the segments are severed from one another by making notches 20, 21 and 22 (FIG. 1). Projections 23, 24 and 25 serve to connect the end connections of a rotor coil to the commutator segments 1, 2 and 3, respectively.

An important factor conductive to the flatness of the commutator structure is that owing to the open chambers in which the collector grooves terminate (see chamber 12, FIG. 2) clamping elements may be disposed in the mould which clamp the segments immediately on either side of the commutator grooves during the formation of the commutator support 11, by injection moulding.

What is claimed is:

1. A commutator structure for a small electrodynamic machine, comprising:

A. an insulative commutator support having a hub member and a plurality of peripherally spaced anchoring elements; and

' B. a plurality of substantially flat metallic elements defining separate and distinct collector segments each having an inner portion and an outer portion, said inner portion of each segment being anchored to said hub member, and said outer portion being connected to said peripheral anchoring elements.

2. The commutator structure of claim 1, wherein the hub member and said peripheral anchoring elements are integrally formed to define a one-piece commutator structure.

3. The commutator structure of claim 1, wherein there are three collector segments, and three anchoring elements.

4. The commutator structure of claim 1, wherein each collector segment is connected to a pair of peripheral anchoring elements.

5. The commutator structure of claim 4, wherein each collector segment shares a peripheral anchoring element with another collector segment.

6. The commutator structure of claim 1, wherein a disc-shaped anti-interference member is disposed upon the hub.

7. The commutator structure of claim 6, wherein each of said collector segments has a lug located upon an outer periphery thereof which is anchored in, and extends through, the commutator support to make contact with said anti-interference member.

8. The commutator structure of claim 1, wherein said collector segments are separated upon the support so as to define grooves therebetween, and further wherein said grooves are positioned over open chambers formed in said support. 

1. A commutator structure for a small electrodynamic machine, comprising: A. an insulative commutator support having a hub member and a plurality of peripherally spaced anchoring elements; and B. a plurality of substantially flat metallic elements defining separate and distinct collector segments each having an inner portion and an outer portion, said inner portion of each segment being anchored To said hub member, and said outer portion being connected to said peripheral anchoring elements.
 2. The commutator structure of claim 1, wherein the hub member and said peripheral anchoring elements are integrally formed to define a one-piece commutator structure.
 3. The commutator structure of claim 1, wherein there are three collector segments, and three anchoring elements.
 4. The commutator structure of claim 1, wherein each collector segment is connected to a pair of peripheral anchoring elements.
 5. The commutator structure of claim 4, wherein each collector segment shares a peripheral anchoring element with another collector segment.
 6. The commutator structure of claim 1, wherein a disc-shaped anti-interference member is disposed upon the hub.
 7. The commutator structure of claim 6, wherein each of said collector segments has a lug located upon an outer periphery thereof which is anchored in, and extends through, the commutator support to make contact with said anti-interference member.
 8. The commutator structure of claim 1, wherein said collector segments are separated upon the support so as to define grooves therebetween, and further wherein said grooves are positioned over open chambers formed in said support. 